The water looks cool for about 5 minutes, and then it kinda gets annoying cause you can't really look at the amzing scenery :3. And if there was lava than it could be really annoying for newbies, and they may even leave the server for good.
Having a waterway under the road sounds cool it can sorta be like a hypothetically secret water way for people to commute in the sewers or take boats so they can travel to spawn... then again that sounds like there could be problems
Would take a lot of resources, but looks really cool. I made flushing trash cans with a sewer system once. It all just drained into the ocean, it was just a flood of dirt xD